I bought these because they were the cheapest version of the same. I don't know if they are really old because my pH hasn't changed in two weeks? I think it's good.
Efficiently Test Your Antifreeze And Battery Acid With A 3-In-1 Refractometer
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Digital PH Meter Tester - Tiaoyeer Water Quality Tester With ATC, 0.01PH High Accuracy, 0.00-14.00 Measurement Range, 0.01 Resolution For Drinking Water, Aquarium, Swimming Pools, Hydroponic
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Portable Handheld Manometer π for Accurate Pressure Differential Measurement
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